A photonic crystal fiber, PCF for short, is a class of optical fiber based on the properties of photonic crystals. Due to the ability to confine light in hollow cores or with confinement characteristics not possible in conventional optical fiber, PCF is finding applications in fiber optic communications, fiber lasers, non-linear devices, high power transmission, highly sensitive gas sensors and in other areas. In the following, PCFs using air holes in their cross sections are also called “holey fiber”.
However, in the fiber structures presently known the ratio of mechanical to thermal sensitivity is currently moderate.
Most existing results on the sensitivity of birefringent microstructured optical fibers (MOF) are results on the polarimetric sensitivity of the MOF to an external perturbation, e.g. pressure or temperature changes. A polarimetric measurement is based on the phase difference of light that has propagated along the two orthogonally polarized modes. The change of this phase difference with the external perturbation is linked with the change in birefringence of the fiber by that perturbation. A polarimetric measurement setup consists of a light source with a controlled polarization and a polarization sensitive detector.
Previous work on the use of fiber Bragg gratings in highly birefringent microstructured optical fibers shows that these sensors can be successfully embedded inside carbon-fiber epoxy laminate composite materials, that they can be sensitive to transverse strain and that they show a temperature sensitivity. This is different from that of FBGs in conventional birefringent fibers. Microstructured optical fibers (MOF) have not featured a high transverse strain sensitivity, i.e. higher than in conventional birefringent fibers. Also the temperature sensitivity of an FBG in such an MOF cannot be tailored. The known fibers show a very low temperature sensitivity.